The present invention relates to an electron beam resist material and more particularly to a method for forming a finely patterned resist layer on a substrate surface using the electron beam resist material.
As is well known, the manufacturing process of various kinds of electronic or semiconductor devices such as ICs, LSIs and the like involves a fine patterning of a resist layer on the surface of a substrate material such as a semiconductor silicon wafer. This fine patterning process is conducted heretofore by the photolithographic method in which the substrate surface is uniformly coated with a positive or negative tone photoresist composition to form a thin layer of the photoresist composition and patternwise irradiation of the photoresist layer with actinic rays such as ultraviolet light followed by a development treatment to selectively dissolve away the photoresist layer in the areas exposed or unexposed, respectively, to the actinic rays leaving a patterned resist layer on the substrate surface. The thus obtained patterned resist layer is utilized as a mask in the subsequent treatment on the substrate surface such as etching.
Whilst the above mentioned patternwise exposure of the resist layer is traditionally conducted with ultraviolet light, the trend in recent years is that, along with the rapid progress of electronic technology toward higher and higher degrees of integration in semiconductor devices, the patterning of the resist layer is required to have an ever increasing fineness which can by accomplished only by using actinic rays having a shorter wavelength than the conventional ultraviolet light. Accordingly, it is now the case that, in place of the conventional ultraviolet light, electron beams, excimer laser beams and X-rays are used as the short-wavelength actinic rays.
As the principle ingredient of a resist material having sensitivity to electron beam irradiation, referred to as an EB resist hereinafter, proposals have been made heretofore for the use of various organic resinous materials such as methacrylic resin-based, polystyrene-based and novolac resin based materials. C60 and its methanofullerene derivatives have previously been shown to be EB resists by the present inventors, Appl. Phys. Lett. volume 72, page 1302 (1998), but these are relatively large molecules. In the polystyrene-based negative-tone EB resist materials, for example, patterning of the resist layer is accomplished by the mechanism that irradiation of the resist layer with electron beams induces crosslinking or polymerization of the resin molecules so that the resist layer is made insoluble in a developer solution in the areas patternwise irradiated with the electron beams leaving a patterned resist layer on the substrate surface so that, as a natural consequence, the fineness of the patterning cannot be finer than the molecular dimensions of the resinous ingredient. In the novolac resin-based EB resist materials the changes in the solubility behaviour of the resist layer in an alkaline developer solution caused by the patternwise irradiation with electron beams is utilized. Again in this case the molecular area of the resinous ingredient is the limiting factor on the fineness of patterning since dissolution of the resist layer in the developer solution proceeds with resin molecules as the dissolving units. Thus, it can be accepted in the prior art that the resolution of patterning cannot be finer than several tens of nanometers at best because the molecules of the above mentioned resins mostly have a molecular size of at least a few nanometers. In the so-called chemical amplification type resist materials recently under development, furthermore, the patterning of the resist layer utilizes a mechanism involving diffusion of the reactive species generated by the irradiation through the resist layer, and it is far from possible therefore to obtain pattern resolution in the ten-nanometer order or finer. Accordingly, it is eagerly desired to develop an EB resist capable of giving higher pattern resolution of nanometer order fineness which would not be obtained with the above described prior art. EB resist systems.
In the methacrylic resin-based positive tone EB resist materials, on the other hand, the pattern resolution is not always under limitation by the molecular size of the resinous ingredient because the patterning of the resist layer is effected by the main chain scission of the resin molecules by the irradiation with electron beams so that a pattern resolution of fineness of about 10 nm has already been obtained. However, the effective fineness of the working resist layer cannot be so high because the resistance of the resist layer against dry etching is relatively poor so that the patterned resist layer cannot be used as formed as a masking resist against etching.
It would be a due guiding principle therefore that the above mentioned defects and problems in the prior art EB resist materials could be overcome when the EB resist comprises, as the principle ingredient, a compound of nanometer order molecular size having a sensitivity to electron beam irradiation and capable of giving a layer having excellent resistance against dry etching.
The present invention, which has been completed as a result of the inventors"" extensive investigations undertaken along the lines of the above mentioned guide principle, has an object to provide a novel EB resist composition as well as a method for the formation of a finely patterned resist layer on a substrate surface utilizing the novel EB resist material by the patternwise irradiation of the resist layer with electron beams.
Thus, the novel EB resist composition provided by the invention comprises a polysubstituted triphenylene compound. The present invention further resides in the use of a polysubstituted triphenylene compound as an electron beam resist material.
A preferred EB resist composition comprises:
(A) an organic solvent; and
(B) a polysubstituted triphenylene compound dissolved in the solvent.
Further, a method of the present invention for the formation of a patterned resist layer on a substrate surface comprises the steps of:
(a) forming a coating layer containing a polysubstituted triphenylene compound on the substrate surface;
(b) irradiating the coating layer patternwise with electron beams; and
(c) selectively removing regions of the thus patternwise irradiated coating layer.
The regions of the patternwise irradiated coating layer which are removed, may be the un-irradiated regions in the case where a negative development is required, or they may be the irradiated regions in the case where a positive tone development is required.
The regions of the patternwise irradiated coating layer are preferably removed by dissolving in an organic solvent.
Preferably, the coating layer is formed by:
(i) coating the substrate surface with a solution of the polysubstituted triphenylene compound in an organic solvent; and
(ii) evaporating the organic solvent from the coating to form the coating layer containing the polysubstituted triphenylene compound.